feat(rumdl): update schema to v0.2.16 (SchemaStore#5811)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: rvben

src/schemas/json/rumdl.json

@@ -6,7 +6,7 @@
   "type": "object",
   "properties": {
     "extends": {
-      "description": "Path to a base config file to inherit settings from.\nSupports relative paths, absolute paths, and `~/` for home directory.\nExample: `extends = \"../base.rumdl.toml\"`",
+      "description": "Path to a base config file to inherit settings from.\nSupports relative paths, absolute paths, `~/` for the home directory, and\n`$VAR` / `${VAR}` environment-variable expansion (a literal `$` is written `$$`).\nExample: `extends = \"../base.rumdl.toml\"` or `extends = \"$GEM_PATH/base.rumdl.toml\"`",
       "type": ["string", "null"]
     },
     "global": {